U.S. patent number 7,289,779 [Application Number 10/381,014] was granted by the patent office on 2007-10-30 for method for calibrating the frequency of an rf oscillator in a mobile part of a mobile communications device.
This patent grant is currently assigned to Siemens Aktiengesellschaft. Invention is credited to Bernd Bienek, Andreas Falkenberg, Stephan Karger, Theo Kreul, Albrecht Kunz, Holger Landenberger.
United States Patent |
7,289,779 |
Bienek , et al. |
October 30, 2007 |
Method for calibrating the frequency of an RF oscillator in a
mobile part of a mobile communications device
Abstract
A method is provided for calibrating the frequency of an RF
oscillator in a mobile part of a mobile communications device when
the mobile part is first switched on, wherein the method includes
the steps of: sampling a modulated carrier that is transmitted by a
base station and has a prescribed frequency accuracy, such that
scanning of the modulated carrier is performed via a frequency
search algorithm with the modulated carrier being demodulated, a
signal thus demodulated being compared in an evaluation and
synchronization program via a correlation with a sequence known in
advance, and a correlation peak in an output of the correlator
being determined; determining a frequency error between the
frequency of the RF oscillator in the mobile part of the mobile
communications device and a known channel frequency of the base
station by comparing the determined correlation peak of the output
of the correlator with a channel raster, known in advance to the
mobile communications device, of the base station; synchronizing
the mobile communications device with the modulated carrier; and
adopting a frequency, corrected by the frequency error, for the RF
oscillator as reference frequency for further calibration
operations.
Inventors: |
Bienek; Bernd (Bocholt,
DE), Falkenberg; Andreas (Escondido, CA), Karger;
Stephan (Hamminkeln, DE), Kreul; Theo
(Coesfeld-Lette, DE), Kunz; Albrecht (Saarbrucken,
DE), Landenberger; Holger (Bocholt, DE) |
Assignee: |
Siemens Aktiengesellschaft
(Munich, DE)
|
Family
ID: |
7656956 |
Appl.
No.: |
10/381,014 |
Filed: |
August 31, 2001 |
PCT
Filed: |
August 31, 2001 |
PCT No.: |
PCT/DE01/03341 |
371(c)(1),(2),(4) Date: |
August 18, 2003 |
PCT
Pub. No.: |
WO02/25812 |
PCT
Pub. Date: |
March 28, 2002 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20040043737 A1 |
Mar 4, 2004 |
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Foreign Application Priority Data
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Sep 20, 2000 [DE] |
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100 46 574 |
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Current U.S.
Class: |
455/147;
375/343 |
Current CPC
Class: |
H03J
1/0066 (20130101); H03J 7/04 (20130101) |
Current International
Class: |
H03J
7/32 (20060101) |
Field of
Search: |
;455/75,87,147,150.1,154.1,158.1,161.1,183.1,184.1,196.1,208,265
;375/343,340 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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25 42 614 |
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Mar 1977 |
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DE |
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39 16749 |
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Nov 1990 |
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DE |
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195 16 449 |
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Nov 1996 |
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DE |
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197 30 521 |
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Feb 1998 |
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DE |
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197 37 758 |
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Mar 1999 |
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DE |
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199 33 542 |
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Jan 2001 |
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DE |
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0 720 298 |
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Jul 1996 |
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EP |
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0 735 675 |
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Oct 1996 |
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EP |
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0 845 860 |
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Jun 1998 |
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EP |
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0 845 860 |
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Jun 1998 |
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EP |
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Primary Examiner: Urban; Edward F.
Assistant Examiner: Nguyen; Tu X.
Attorney, Agent or Firm: Bell, Boyd & Lloyd LLP
Claims
The invention claimed is:
1. A method for calibrating a frequency of an RF oscillator in a
mobile part of a mobile communications device when the mobile part
is first switched on, the method comprising the steps of: sampling
a modulated carrier that is transmitted by a base station and has a
prescribed frequency accuracy, wherein a scanning of the modulated
carrier is performed via a frequency search algorithm with the
modulated carrier being demodulated, a signal thus demodulated
being compared in an evaluation and synchronization program via a
correlator with a sequence known in advance, and a correlation peak
in an output of the correlator being determined; determining a
frequency error between the frequency of the RF oscillator in the
mobile part of the mobile communications device and a known channel
frequency of the base station by comparing the determined
correlation peak of the output of the correlator with a channel
raster, known in advance to the mobile communications device, of
the base station; synchronizing the mobile communications device
with the modulated carrier; and adopting a frequency, corrected by
the frequency error, for the RF oscillator as reference frequency
for further calibration operations.
2. A method for calibrating a frequency of an RF oscillator in a
mobile part of a mobile communications device as claimed in claim
1, wherein the method is carried out under a UMTS Standard, with
the sequence being a pSCH sequence uniform throughout an associated
network.
3. A method for calibrating a frequency of an RF oscillator in a
mobile part of a mobile communications device as claimed in claim
1, wherein the method is carried out repeatedly, starting out from
the respective reference frequency last determined.
4. A method for calibrating a frequency of an RF oscillator in a
mobile part of a mobile communications device as claimed in claim
1, wherein, for a first synchronization of a transmitted signal,
use is made of an arbitrary base station and, for a subsequent
callup, use is made of a carrier of another base station.
5. A method for calibrating a frequency of an RF oscillator in a
mobile part of a mobile communications device as claimed in claim
4, wherein a single multi-mobile part is used for synchronizing the
mobile communications device with mutually synchronized base
stations of different standards.
6. A method for calibrating a frequency of an RF oscillator in a
mobile part of a mobile communications device as claimed in claim
1, the method further comprising the step of performing a
calibration over a temperature range via a temperature measurement.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a method for calibrating the
frequency of an RF oscillator in a mobile part of a mobile
communications device when the mobile part of the mobile
communications device is first switched on, having the following
steps: sampling a modulated carrier that is transmitted by a base
station and has a prescribed frequency accuracy; determining the
frequency error between the frequency of the RF oscillator in the
mobile part of the mobile communications device and a known channel
frequency of the base station; and synchronizing of the mobile
communications device with the modulated carrier.
Such a method is disclosed in EP 0 735 675 A2, the determination of
the sequence error being performed successively by virtue of the
fact that the search range for the frequency of the base station is
expanded until the frequency of the base station is found. The
channel frequency of the base station is certainly fundamental, but
not known on the part of the mobile communications device.
Depending on the transmission method, the field of mobile
communication is generally covered by a certain standard that
requires a prescribed frequency accuracy for a base station of a
communications device during transmission and prescribes a
frequency accuracy for the case of reception in the mobile receiver
part via further system properties.
This standard has been ensured to date by calibrating the RF
oscillator during fabrication of the mobile part of a mobile
communications device. However, calibration in fabrication is very
expensive and requires a long production time.
It also has been proposed, for the purpose of correcting the
temperature dependence of an RF oscillator in a mobile part of a
mobile communications device, to make use of a temperature sensor
that compensates the temperature-dependent error of the RF
oscillator in conjunction with an appropriate algorithm. This
method is also very expensive.
It is, therefore, an object of the present invention to propose a
method by which the production costs for a mobile communications
device are lowered and, at the same time, a reliable calibration of
the frequency of the RF oscillator of the mobile part of the mobile
communications device is ensured.
SUMMARY OF THE INVENTION
The present invention is based on the fundamental idea that the
calibration of the RF oscillator can be performed by the customer
when a mobile receiver is switched on for the first time. Use is
made for this purpose of the accuracy of the transmit frequency of
a base station, which accuracy is specified with sufficiently high
accuracy and by standardization bodies. The transmitted carrier,
with information modulated thereon, which is transmitted by the
base station, is scanned in the mobile receive section. If the
transmitted carrier, whose frequency is known a priori with high
accuracy through the channel raster, is received, with the
information modulated thereon, with a satisfactory frequency
accuracy, the frequency error can be determined and the mobile part
of the mobile communications device can be synchronized with the
carrier. The frequency corrected by the frequency error is then
used as reference frequency. Instead of the initial calibration
during the production process of the mobile part, the required
settings are undertaken during the first startup via the frequency
search algorithm. The calibration is therefore performed fully
automatically.
It is advantageous to carry out the method according to the present
invention repeatedly; in particular, with each xth callup, starting
in each case from the reference frequency last determined. It is
then possible to assume a smaller frequency deviation of the RF
oscillator in these later synchronization operations. As a rule,
the method according to the present invention is not carried out
again immediately, since it may be assumed that the RF oscillator
has been effectively calibrated by the previous initial
autocalibration. The dummy x is a function, inter alia, of
temperature fluctuations in the surroundings of the oscillator, and
of its age. Consequently, the dummy x certainly can be 1, but is
not constrained to be so. The future synchronization is thereby
accelerated. Moreover, the accuracy is increased by averaging a
number of measurements. In addition, the speed of the
synchronization is increased by virtue of the fact that only a
relatively small frequency band has to be scanned. The power
consumption in the mobile part is reduced by a quicker
synchronization, and this leads to a longer period of use. It is
thereby possible, in addition, to recalibrate aging effects and
temperature deviations of the components that are required for
frequency generation. This can take place, for example, with each
xth callup and, consequently, it does not cause any additional
outlay. The recalibration also substantially lengthens the product
service life without additional outlay.
It is also advantageous when use is made during the first
synchronization of a transmitted signal of an arbitrary base
station of sufficient accuracy, but the subsequent callup is
performed on a carrier of another base station of sufficient
accuracy. This signal can have a better signal-to-noise ratio, and
can deliver a higher frequency accuracy as well as a shorter
synchronization time. For example, it is possible in the case of
the UMTS method to make use of each of the possible channels of the
UMTS network for autocalibration. It is thereby possible to
synchronize with an arbitrary channel of a specific base station of
an operating company. The subsequent callup can then take place on
an arbitrary channel, including another one with another operating
company. It is likewise possible to carry out the synchronization
and the callup with the same base station when the latter is the
most suitable one at the time.
Furthermore, in the case of a further embodiment of the present
invention, a single multimode mobile part can be used for
synchronizing the mobile communications device with mutually
synchronized base stations of different standards. This leads to a
synchronization that is simple, fast and versatile. Moreover, many
different standards can be interconnected thereby.
Furthermore, it is advantageous when the calibration additionally
takes place over the temperature range, for which purpose a
temperature measurement is combined with the frequency search
algorithm. Such a calibration over the temperature would be
particularly time-consuming and cost-intensive to produce. Owing to
the continuous variation of the surroundings of the mobile part, a
constant and optimum adaptation to the current circumstances can be
performed by such a calibration during the frequency
acquisition.
Additional features and advantages of the present invention are
described in, and will be apparent from, the following Detailed
Description of the Invention and the Figures.
BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 shows a systematic illustration of a method according to the
present invention.
FIG. 2 shows a simulation result from the method illustrated in
FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
The method illustrated in FIG. 1 is explained by way of example
with the aid of an application in the UMTS Standard.
Synchronization to an accuracy of +/-3 ppm with regard to the
carrier frequency used is required in UMTS, in order to be able to
undertake subsequent temporal synchronization. An RF oscillator of
a production series has on average a component scatter of typically
+/-25 ppm in the natural frequency. This is then reduced to a
natural frequency scatter of +/-3 ppm by the autofrequency
calibration described below. A mobile part 1 of a mobile
communications device receives a signal 4, transmitted by a base
station (not illustrated) in a receiver 5. The transmitted signal 4
is from the baseband of the base station, which is arranged around
approximately 2. 1 GHz. The received signal 4 is demodulated in a
known manner, and the signal 6 thus demodulated is compared in an
evaluation and synchronization program 3 via a correlator with the
pSCH sequence, which is already known in advance and uniform
throughout the network. In this case, pSCH stands for Primary
Synchronization Channel in accordance with the UMTS Standard.
FIG. 2 shows the output 12 of the correlator in the baseband, the
frequencies illustrated being reduced by the center carrier
frequency of the base station. A correlation peak 13 is formed at a
frequency of 10 MHz. The mobile station in which channel raster the
base station is transmitting is known a priori. At the base station
end, the carrier frequency can support radio signals such as, for
example, DCF77 or GPS with an accuracy that is still below that of
the specification of the UTMS Standard of 0. 05 ppm. The deviation
of the RF oscillator 2 of the mobile station 1 can be determined
from the comparison of the known channel frequency of the base
station with the measured correlation peak 13 of the output 12 of
FIG. 2. The data for the autocalibration are obtained therefrom.
The production-induced scatters in the natural oscillator frequency
of the RF oscillator 2 of +/-25 ppm thereby can be compensated to
the extent that it is possible to assume a maximum deviation of
+/-3 ppm for future synchronization operations. Future
synchronization processes are substantially accelerated thereby.
This saves time and reduces the energy required for calibration,
something which reduces the power consumption and thereby permits
longer standby times of the mobile part.
Digital settings are obtained via the step, illustrated in FIG. 1,
of the comparison in the evaluation and synchronization program 3.
During a synchronization, the settings are passed on via a switch 7
to a memory 8 in which these are stored. The digital settings are
also passed on to a digital-to-analog converter 9. The latter
passes on the analog signal, which corresponds to the digital
settings, to the voltage-controlled RF oscillator 2. On the one
hand, the digital settings are passed on to further modules 11 and,
on the other hand, they are passed on as new reference frequency
f.sub.ref to the receiver 5 via a line 10.
On the occasion of the next calibration, this new reference
frequency f.sub.ref serves as reference signal for the signal 4
then received, which is transmitted by the base station. A new
calibration is undertaken using the steps set forth above after the
demodulation of the demodulated received signal 6, passed on by the
receiver 5, in relation to the evaluation and synchronization
program 3. In which case, the synchronization can be performed more
quickly, since the current reference frequency f.sub.ref is
affected by a smaller scattering value.
Although the present invention has been described with reference to
specific embodiments, those of skill in the art will recognize that
changes may be made thereto without departing from the spirit and
scope of the present invention as set forth in the hereafter
appended claims.
* * * * *